1. Field of the Invention
Embodiments of the present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a method of fabricating the same. Although embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for obtaining a rapid response speed and a high aperture ratio.
2. Discussion of the Related Art
In general, active matrix (AM) LCD devices have high speed and are widely used for flat type televisions, mobile computers and monitors. Among the AM LCD devices, a twisted nematic (TN) mode LCD device is typically used, in which two electrodes are respectively formed on two substrates. When a voltage is applied across the two electrodes, directors of the liquid crystal are realigned with a twist of 90°. The TN mode LCD device has attracted attention due to its advantageous display properties, such as great contrast and high resolution. However, the TN mode LCD device also has the problem of a narrow viewing angle.
To overcome this problem of TN mode LCD device having a relatively narrow viewing angle, other devices have been proposed for use, such as in-plane switching (IPS) mode LCD device and fringe field switching (FFS) mode LCD device. In the IPS mode LCD device, two electrodes are formed on one substrate such that the directors of the liquid crystal are twisted between surfaces of alignment layers. In the FFS mode LCD device, common and pixel electrodes are formed of transparent conductors and a small interval is maintained between the common and pixel electrodes such that liquid crystal molecules are driven by a fringe field generated between the common and pixel electrodes.
Both the IPS and FFS modes have a similar operation method in that each of the IPS and FFS modes includes the electrodes formed on one substrate that receive the applied operating voltages. However, the arrangement of electrodes of the IPS mode is different from that of the FFS mode. Hereinafter, a related art LCD device will be described with reference to the accompanying drawings.
FIG. 1 is a plan view of illustrating the related art FFS mode LCD device. Referring to FIG. 1, the related art FFS mode LCD device includes gate lines 3 and data lines 7 of opaque metal crossing each other to define a pixel region (P), a common line 10a parallel to the gate line 3, a thin film transistor (TFT) adjacent to the crossing of the gate lines 3 and data lines 7, a counter electrode 2 having a plate shape formed and made of a transparent conductor in the pixel region (P), and a pixel electrode 9a overlapping the counter electrode 2 and having the shape of comb including a plurality of teeth.
The thin film transistor (TFT) includes a semiconductor layer (not shown) formed over a predetermined portion of the gate line 3, a source electrode 7a protruding from the data line 7, and a drain electrode 7b formed at a predetermined interval from the source electrode 7a. The source and drain electrodes 7a and 7b are positioned at both sides of the semiconductor layer. The pixel electrode 9a is formed as one body with an extension part 9b so that the pixel electrode 9a is electrically connected with the drain electrode 7b such that the respective end portions corresponding to the comb teeth of pixel electrode 9a are connected with one another by the extension part 9b. Thus, the drain electrode 7b is electrically connected with the extension part 9b by the contact part.
The common line 10a includes common electrodes 10b, which are positioned adjacent to the data lines 7 at the both sides of pixel region P. The common line 10a and common electrode 10b is electrically connected with the counter electrode 2. At this time, the common electrode 10b is offset from the pixel electrode 9a and a portion of counter electrode 2.
In the FFS mode having the above-mentioned electrode structure, the counter electrode 2 is formed throughout the pixel region (P), and the counter electrode 2 is formed in a different layer from the pixel electrode 9a. Thus, the fringe field is formed between the pixel electrode 9a and the counter electrode 2, wherein the fringe field is formed with the electric field being curved toward the counter electrode 2 from the center of pixel electrode 9a. The electric field may be also formed in the overlap portion between the counter electrode 2 and the pixel electrode 9a. As the LCD device is turned-on, the liquid crystal is largely moved based on the electric field. A large operating voltage is required because the liquid crystal molecules need to be greatly moved. Unless the operating voltage is sufficiently large to control the liquid crystal, the response speed is relatively lower so that an afterimage phenomenon occurs.
As shown in the drawings, the plurality of pixel electrodes 9 may be connected with one another by the extension part 9b formed at one end of pixel electrode 9. In addition, another extension part having a bar shape may be formed at the other end of pixel electrode 9. That is, the pixel electrode 9 may be a plate provided with a plurality of slits. To solve the afterimage problem, the IPS mode LCD device is more widely used.
FIG. 2 is a plan view of illustrating the related art IPS mode LCD device. Referring to FIG. 2, the related art IPS mode LCD device includes gate lines 21 and data lines 20 crossing each other to define a pixel region (P), a thin film transistor (TFT) which is formed adjacent to the crossing of the gate lines 21 and data lines 20 to switch on/off a voltage, pixel electrodes 28a and common electrode 29a alternate with each other in the pixel region (P), a common line 22 is formed parallel to the gate line 21, an extension part 28 electrically connects the a drain electrode of thin film transistor with the pixel electrodes 28a as one body, and a common electrode connection part 29 connects the common electrodes 29a as one body. The thin film transistor (TFT) includes a gate electrode 23 which protrudes from the gate line 21, a semiconductor layer (not shown) over the gate electrode 23, a source electrode 25 protruding from the data line 20, and a drain electrode 27 positioned at a predetermined interval from the source electrode 25. The source and drain electrodes 25 and 27 are positioned at both sides of the semiconductor layer.
In the related art IPS mode LCD device of the above-mentioned structure, the IPS mode electric field occurs between the pixel electrodes 28a and the common electrodes 29a that alternate with each other at intervals, whereby the liquid crystal molecules are driven by the IPS mode electric field. In this case, the liquid crystal molecules are not smoothly driven just above the pixel electrodes 28a and the common electrodes 29a since the electric field is not formed above the pixel electrodes 28a and the common electrodes 29a. 
Accordingly, the related art LCD device has the following disadvantages. While applying the voltage across the common and pixel electrodes in the related art IPS mode LCD device, the in-plane electric field is not formed just above the common and pixel electrodes. Thus, the liquid crystal molecules are not properly driven just above the common and pixel electrodes such that the aperture ratio and light transmittance are lowered. In the related art FFS mode LCD device where the counter electrode of plate shape is formed throughout the area of pixel region, and slitted or fingered pixel electrode is formed thereon, a large operating voltage is required to move the liquid crystal molecules. Unless the operating voltage is sufficiently large to control the liquid crystal, the response speed of liquid crystal is low and it is difficult to obtain the rapid response speed for displaying moving images. As a result of not obtaining a rapid response speed, an afterimage can occur on the display panel.